The present invention relates to a gas insulated switchgear and, in particular, relates to a gas insulated switchgear in which arrestors are connected to corresponding gas insulated main buses.
A surge voltage coming into a substation from a power transmission line is generally limited in its peak value through the operation of an arrestor, and thereafter reaches terminals of respective electrical machines and apparatuses. However, when the distance between the arrestor and the terminal of an electrical machine and apparatus to be protected is long, reflection waves are caused at the respective terminals of the electrical machines and apparatuses, and a higher voltage than the limiting voltage of the arrestor caused by superposition of the reflection waves is applied to the respective electrical machines and apparatuses.
Since the deviation therebetween increases as the distance between the arrestor and the terminal of the electrical machine and apparatus to be protected increases, it is necessary to dispose an arrestor as close as possible to the electrical machine and apparatus to be protected in order that the arrestor fully achieves its protective effect. Further it is understood that if the distance is within 50 m, a sufficiently protective performance of the arrestor is achieved. In a normal substation, arrestors are disposed at a power transmission line lead-in port; however, in the of a large scale substation, in particular a substation for a 1000 KV power transmission system, the distance from the power transmission line lead-in port to an opened contact end portion of a circuit breaker may exceed 50 m, which necessitates to additional arrestors at gas insulated main buses other than at the power transmission line lead-in port.
JP-B-63-38924(1988) discloses. An example of a phase isolated double bus type gas insulated switchgear. A proposed application of arrestor units to the switchear shown is explained with reference in FIG. 7 of this publication is explained with reference to FIG. 4 through FIG. 6 of the present drawings.
First main buses 1A, 1B and 1C and second main buses 2A, 2B and 2C of phase isolated type gas insulated main buses are arranged over substantially the same plane, in substantially in parallel, and with substantially the same spacing. The first main buses 1A, 1B and 1C and the second main buses 2A, 2B and 2C are connected to a power transmission line via line use gas insulated switchgear units 3A, 3B, 3C, disconnecting switches 4A, 4B, 4C and 5A, 5B, 5C and line buses 6A, 6B, 6C. Similarly, the first main buses 1A, 1B, 1C and the second main buses 2A, 2B, 2C are connected to a transformer via transformer-use gas insulated switchgear units 7A, 7B, 7C, disconnecting switches 8A, 8B, 8C and 9A, 9B, 9C and transformer connection buses 10A, 10B, 10C. Further, the first main buses 1A, 1B and 1C are connected with the second main buses 2A, 2B and 2C via bus-connection-use gas insulated switchgear units 11A, 11B, 11C, disconnecting switches 12A, 12B, 12C and 13A, 13B, 13C and connecting buses 14A, 14B, 14C. These connecting buses 14A, 14B, 14C are arranged to extend over the switchgear units in two layers so as to reduce the installation area of the gas insulated switchgear.
The size of a gas insulated switchgear constituted by such main constitutional components is huge and the distance from the arrestors which are normally disposed at the power transmission line lead-in port to the open-end portions of the circuit breakers in respective switchgear units exceeds 50 m. Therefore, for the reason explained above, arrestors 15A, 15B, 15C and 17A, 17B, 17C are disposed at positions in which the distance from the open-end portions of the circuit breakers in the respective switchgear units does not exceed 50 m. These arrestors are connected to respective corresponding main buses 1A, 1B, 1C and 2A, 2B, 2C via arrestor-connection-leading-out buses 16A, 16B, 16C and 18A, 18B, 18C.
In an arrangement of these arrestors, the distance between the arrestors 15A, 15B, 15C and the outermost main bus 1A among the plurality of the main buses, and the distance between the arrestors 17A, 17B, 17C and the outermost main bus 2C were determined to be substantially the same for the respective three phases. As a result, the three-phase arrestors were arranged substantially linearly along the axial direction of the main buses, and the area or width required for installing the the three phase arrestors absolutely depended on the size of a single arrestor.
However, due to the recent appreciation of land values, it has become difficult to obtain a necessary site for a substation, which forces to construction of electrical machines and apparatuses for the substation to be more compact.